1. Field of the Invention
The present invention relates to a method and apparatus for bonding a metal needle to a plastic tubing and the needle assembly formed thereby.
2. Description of the Prior Art
Heretofore various techniques have been proposed for securing a needle to a plastic part. Such techniques have included molding a plastic part onto the needle and wedging or swagging a plastic part onto a needle. Examples of such techniques are disclosed in U.S. Pat. Nos. 2,091,438 and 3,964,857.
Also it has been known to use heat sealing techniques for sealing or welding plastic parts together. Examples of such heat sealing techniques are disclosed in U.S. Pat. Nos. 3,300,559, 3,128,504, 3,509,252 and 3,929,943.
Moreover various techniques utilizing an adhesive, heat, solvents or molding techniques for securing a needle to a plastic part have been proposed. Examples of these techniques are disclosed in U.S. Pat. Nos. 3,523,531, 3,523,532, 3,523,533, and 3,640,275.
With the various techniques heretofore proposed there has occurred a problem in the integrity of the bond of the plastic part to the needle. More specifically, the bonds previously achieved by molding, wedging, or using an adhesive, solvent or heat have not provided a strong hermetic seal between the needle and the plastic tubing. Accordingly there was a limitation on the push-pull forces that could be applied to the bond when the needle was inserted or withdrawn from a patient. Also there was a limitation on the pressure of the fluid that could be applied through the tubing and needle assembly. In this respect prior bonds between a needle and a plastic part such as a tubing have not always been able to withstand pressures up to 30 psi.
Another technique heretofore utilized for securing a needle to the end of a plastic tubing was to apply a cement to the inner end of the needle and to apply a solvent such as cyclohexanone to the interior of the tubing. Then the tubing is placed on the end of the needle and the needle assembly formed thereby is placed in a heat chamber to sterilize the needle and at the same time to evaporate the solvent. This technique is slow and cumbersome, often resulted in marring of the outer surface of the tubing with the solvent, and did not provide a bonding having the desired integrity. That is to say, the push-pull strength and the fluid pressure which the resulting needle assembly could withstand did not meet the desired levels.
As will be explained in greater detail hereinafter, the present invention provides a method for bonding the end portion of a plastic tubing to a needle and an apparatus for carrying out the method by means of which a needle assembly is obtained wherein the integrity of the bond between the needle and the plastic tubing has the desired strength and hermetic sealing. More specifically, the needle assembly has a bond which provides a strong mechanical bond and a strong hermetic seal such that the push-pull strength of the needle assembly and the fluid pressure which the needle assembly can withstand meet the levels desired.